A method for a user to advise related entities with respect to a consumer service of their contact details wherein the user submits data to a Contact Details Registration Service to register their use of the consumer service; the Contact Details Registration Service allocating the user with a unique identification indicia and transmitting same to the user for subsequent use in communications with the Contact Details Registration Service and/or any related entities of the consumer service registered with the Contact Details Registration Service; the data submitted by the user including their contact details and having at least an address to which correspondence is to be sent, the contact details being associated with the unique identification indicia of the user by the Contact Detail Registration Service and stored in a database; and the user's contact details being accessible to the consumer service, or related entities thereof, upon provision of the user's associated unique identification identifier to the Contact Details Registration Service database, wherein the Contact Details Registration Service database maintains a record of related entity requests for the contact details of the user.